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STLC3055Q

WLL & ISDN-TA SUBSCRIBER LINE INTERFACE CIRCUIT

STMicroelectronics 

STLC3055

Figure 5. TIP/RING typical ringing waveform

GND

TIP

2.5V typ.

65V

typ.

dV/dT set

by CREV

RING

VBAT

2.5V typ.

obtained with a 20Hz and 25Hz ring frequency

and with 1REN. This value are valid either with

European or USA specification:

CREV

22nF

27nF

33nF

CREST

FACTOR

@20Hz

1.2

1.25

1.33

CREST

FACTOR

@25Hz

1.26

1.32

Not significant (*)

(*) Distorsion already less than 10%.

If for any reason the ringer load will be too high

the self generated battery will drop in order to

keep the power consumption to the fixed limit and

therefore also the ring voltage level will be re-

duced.

In the typical application with RSENSE = 110mΩ

the peak current from Vpos is limited to about

900mA, which correspond to an average current

of 700mA max. In this condition the STLC3055

can drive up to 3REN with a ring frequency

fr=25Hz (1REN = 1800Ω + 1.0µF, European

standard).

In order to drive up to 5REN (1REN= 6930Ω +

8µF, US standard) it is necessary to modify the

external components as follows:

CREV = 15nF

RD = 2.2KΩ

Power On Requirements

In order to avoid damage to the device when

Vpos is first applied it is recommended to keep all

the logic inputs to a low logic level (0V) until Vpos

is >5.5V.

In case this power up sequence cannot be guar-

anteed it’s recommended to connect a shottky di-

ode (BAT46 or equivalent) between VBAT and

BGND see figure below.

The ring trip detection is performed sensing the

variation of the AC line impedance from on hook

(relatively high) to off-hook (low). This particular

ring trip method allows to operate without DC off-

set superimposed on the ring signal and therefore

obtaining the maximum possible ring level on the

load starting from a given negative battery.

It should be noted that such a method is opti-

mised for operation on short loop applications and

may not operate properly in presence of long loop

applications (> 500Ω ).

Once ring trip is detected, the DET output is acti-

vated (logic level low), at this point the card con-

troller or a simple logic circuit should stop the D2

toggling in order to effectively disconnect the ring

signal and then set the STLC3055 in the proper

operating mode (normally ACTIVE).

Figure 6. Shottky diode connection

BGND

STLC3055

VBAT

BAT46

RING LEVEL IN PRESENCE OF MORE TELE-

PHONE IN PARALLEL

As already mentioned above the maximum cur-

rent that can be drawn from the Vpos supply is

controlled and limited via the external RSENSE.

This will limit also the power available at the self

generated negative battery.

8/22

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